The present invention relates to a turbo-charger with a rotary machine to be rotated at a high speed.
In recent years, it has become practical to equip internal combustion engines with turbo-chargers each having a turbine rotatable by engine exhaust gases to compress engine intake air to supercharge an engine. It has also been thought of to utilize the thermal energy of engine exhaust gases to produce supercharging air as well as to generate an electric power. More specifically, a device is thought of which includes a turbo-charger having a turbine shaft connected with not only a compressor but also a rotor which is formed by a permanent magnet capable of withstanding magnetic reduction at a high temperature. The device also includes a stator disposed around the rotor with a predetermined gap formed therebetween. An example of such device is disclosed in U.S. Pat. No. 4,253,031.
It is also proposed that, in the case where the thermal energy possessed by engine exhaust gases is so high that the power generated by a turbo-charger turbine cannot be fully spent by a supercharging compressor, the surplus thermal energy is utilized to drive a rotary machine formed by a rotor and a stator to cause the machine to generate an electric power and that, in the case where the thermal energy of the engine exhaust gases is so low that the power generated by the turbine is insufficient to drive the supercharging compressor, the rotary machine is electrically energized by an electric power source to cause the machine to act as an electric motor. This art is disclosed in, for example, Japanese Unexamined Patent Publication No. 62-254649.
Such turbo-chargers are, in general, rotated at a super high speed. Thus, when a dynamic unbalance is caused in the rotor of the rotary machine on a turbo-charger during a high speed operation thereof, there is a possibility that the turbine shaft suffers from a bending vibration which would cause a resonance resulting in a breakdown as a whole, of the turbo-charger.